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This article mainly introduces "how to achieve abstract factory pattern in Python". In daily operation, I believe many people have doubts about how to achieve abstract factory pattern in Python. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the doubts of "how to realize abstract factory pattern in Python". Next, please follow the editor to study!

Reality

2) create a product AbstractFactory only declares an interface for creating a product, and the real creation of a product is made by the

Implemented by the ConcreteProduct subclass. One of the most common approaches is to define a factory method for each product (see Factory Method (3. 3)). A specific factory will redefine the factory method for each product to specify the product. Although this implementation is simple, it requires each product family to have a new specific factory subclass, even if the differences between these product families are small.

If there are multiple possible product lines, the specific factory can also use the Prototype (3.4) pattern to implement. The specific factory is initialized with a prototype instance of each product in the product family, and it creates a new product by copying its prototype. In a prototype-based approach, not every new product line requires a new concrete factory class.

The following is an example of a prototype-generated object in Smalltalk, which is omitted here. Smalltalk is a magical language that needs to be mentioned in classic object-oriented books, but has never seen where it is actually used. Let's still provide an example of C++. As usual, look at the class diagram first:

CustomThemeFactory reads the topic information saved in the file and generates a prototype.

When createWindow and createScrollbar are called, the code clones the specific product from CustomWindow,CustomScrollbar, respectively. By specifying different files, we can produce any group of products.

3) defining an extensible factory AbstractFactory usually defines an operation for each product it can produce. The type of product is coded in the operational configuration. Adding a new product requires changing the interface of AbstractF actory and all the classes associated with it. A more flexible but less secure design is to add a parameter to the operation of creating an object. This parameter specifies the type of object that will be created. It can be a class identifier, an integer, a string, or anything else that identifies the product. In fact, using this method, AbstractFactory only needs a "Make" operation and a parameter indicating the kind of object to be created. This is the prototype-based and class-based abstraction factory discussed earlier.

The technology.

Compared with statically typed languages such as C + +, this change is easier to use in dynamically typed languages such as Smalltalk. You can use it in C + only if all objects have the same abstract base class, or when product objects can be safely cast to the correct type by their customers. The implementation section of Factory Method shows how to implement such a parameterized operation in C + +.

Even if this method does not require type casting, there is still an essential problem: all products return the same abstract interface given by the return type to the customer. Customers will not be able to distinguish or make safety assumptions about the category of a product. If a customer needs to perform operations related to a specific subclass, these operations cannot be obtained through an abstract interface. Although customers can implement a downward type conversion (downcast) (such as using dynamic_cast in C + +), this is not always feasible or safe because downward conversion may fail. This is a typical tradeoff between highly flexible and extensible interfaces.

You can choose to re-understand this part after learning the Factory Method pattern. But one thing is certain: when we need to complete multiple similar functions, using parameter differentiation or writing multiple functions directly is definitely one of the sources of programmers' annoyance. Compromise, trade-off and compromise all mean the same thing.

At this point, the study on "how to implement the abstract factory pattern in Python" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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